1. Field of Invention
The present invention relates to the field of an infrared detector and an electronic material, and more particularly to a vanadium oxide thermo-sensitive film material with high temperature coefficient of resistance and a preparing method thereof.
2. Description of Related Arts
Due to advantages such as high temperature coefficient of resistance, low noise, good processing compatibility in Micro-Electro-Mechanical Systems (MEMS) and integrated circuit compatibility, vanadium oxide film is widely used as a thermo-sensitive material for high performance uncooled Focal Plane Array (UFPA). According to the noise theory of UFPA devices, the temperature coefficient of resistance (TCR) and the noise figure of the vanadium oxide thermo-sensitive film are two of main factors which influence sensitivity of the device. The higher the TCR of the vanadium oxide thermo-sensitive film, the smaller the noise figure, and accordingly the small the noise equivalent temperature difference (NETD) of the UFPA devices, i.e., the higher the sensitivity of the devices. In addition, the TCR of semiconductor materials is usually a negative value, and the values of TCR in the present invention are all referring to the absolute value of the TCR.
As an important metallic oxide semiconductor material, vanadium oxide is capable of forming up to 13 stable phases. Due to difference in atomic arrangement of each phase, the properties of vanadium oxide in different phases are greatly different, which causes a result that preparation of vanadium oxide thermo-sensitive film becomes one of the difficulties in high performance UFPAs. The commonly-used vanadium oxide thermo-sensitive film in UFPAs is mixed-valence vanadium oxide (VOx) film, wherein the oxygen content has to meet a certain requirement to obtain an appropriate electrical resistivity and overall performance of the films, so as to assure a good performance of the devices. The mixed-valence vanadium oxide film usually has 2.0-2.5%/K TCR (R. A. Wood, et al., IEEE, 1992, 132-135; S. H. Black, et al., Proc. of SPIE, 2011, 8012, 80121A). However, the resistance stability of this kind of mixed-valence vanadium oxide film is poor. As a result, a passivation protection layer made of dielectric films such as SiNx is further required after the deposition of the mixed-valence vanadium oxide film, in order to avoid obvious changes of the resistance of the film during the interval of process-transfer or during the subsequent process. Moreover, the instability of the mixed-valence vanadium oxide film indicates a stricter requirement for the preparation process of the passivation protection layer, so as to avoid changes of the resistance of the mixed-valence vanadium oxide film during the deposition process of the passivation protection layer. All these conditions result in the difficulty of MEMS-process compatibility of manufacturing UFPAs.
Among the different phases of vanadium oxide, since TCR of VO2 films in the semiconductor-metal phase transition region is over 16%/K, ones try to use VO2 film with semiconductor-metal phase transition as the thermo-sensitive material for UFPAs, but the hysteresis phenomenon during the phase transition means a high thermal hysteresis noise. On the one hand, thermal hysteresis noise will apparently increase the noise of the UFPA device, thus decrease the signal-to-noise ratio. On the other hand, during the preparation process of UFPAs, the process temperature of several subsequent processes following the deposition of thermo-sensitive film, such as Plasma Enhanced Chemical Vapor Deposition (PECVD) process of the dielectric layer, the process for removing of photoresist, and the release process of sacrificial layer materials, is far larger than the phase-transition temperature of VO2 film. This means that the VO2 film will go through repeatedly phase transition during the device manufacturing process. The phase transition accompanies with the change of the volume of VO2 films. As a result, the repeatedly volume changes will inevitably decrease the reliability of multi-layer films of the UFPA microbridge. Therefore, it is difficult for one to use VO2 films as the thermo-sensitive material in the development of the UFPA devices with high performance.
Thus, in order to meet the demands of manufacturing the UFPAs with high performance, it is important to develop a new type vanadium oxide film material with high TCR, high resistance stability, no phase transition, and low noise.
The reference CN101552048A with a title “Yttrium-doped zinc oxide (ZnO:Y) transparent conductive film and a preparing method thereof” discloses that zinc oxide serves as host material and yttrium serves as dopant to prepare conducting film, so as to improve photoelectric property of the conducting film material. The present invention aims at the main problems of vanadium oxide thermo-sensitive film in the process of fabricating UFPA devices, and thus is different from the technical problems and the beneficial effects of yttrium serving as dopant in the reference. Furthermore, though yttrium-doping is applied in other oxide material, yttrium-doping is not disclosed for vanadium oxide host material.